Histone modifications play an important role in transcription regulation by modulating chromatin structure. Histone H3 methylation demarcates regions of transcriptionally active chromatin from transcriptionally silenced heterochromatin. Set1, Set2, and Dot1, the histone methyltransferases which methylate histone H3 residues 4, 36 and 79 respectively, can catalyze the addition of 1, 2 or 3 methyl groups to the epsilon amino group of the lysine residue. While individual methylation events have been studied extensively, the enzymes themselves have not been completely characterized. Further, little is know about the role of combinations of methylation events and their effects on gene expression and chromatin structure. These 3 enzymes will be kinetically characterized on reconstituted nucleosome substrates. The effects of adjacent histone methylation events, ubiquitation of histone H2B, and acetylation, on the activity of these enzymes will be examined. The effects of combinations of methylation events on gene expression and chromatin structure will be determined by microarray analysis and micrococcal nuclease assays.